Androgen and estrogen receptors in bovine skeletal muscle: relation to steroid-induced allometric muscle growth.

The presence of free androgen (AR) and estrogen receptors (ER) was demonstrated in bovine skeletal muscle. Androgen receptor concentrations in neck muscle from cattle of different sexes and stages of development were related to hormonal status. In mature bulls (mean weight 600 kg), no free AR was detectable. Highest AR concentrations were measured in mature bulls (517 kg) castrated 24 h prior to slaughter (.85 +/- .21 fmol/mg protein). In female calves (155 kg), AR concentrations (.56 +/- .14 fmol/mg) were greater (P less than .01) than in male calves (.20 +/- .08 fmol/mg) of the same weight. Androgen receptors and ER in skeletal muscle of neck, shoulder, abdomen and hind leg of female and male calves were compared. There was no significant difference between AR concentrations in the neck, shoulder and hind leg, but concentrations were lower (P less than .05) in abdominal muscle. Estrogen receptor concentrations in neck, shoulder, abdomen and hind leg were not different between sexes (P less than .05). In male calves, ER content was lower (P less than .05) in abdominal than in other muscles. Estrogen receptor concentrations in muscles of female calves did not differ (P less than .05). The pronounced sensitivity to estrogens and androgens in the neck, shoulder, and hind leg of calves, being free of the respective hormone, may partly explain the characteristic conformation in calves treated with estrogenic and androgenic steroids and the sexual dimorphism of muscle growth.